All cases of TB are passed from person to person via droplets. When someone with TB infection coughs, sneezes, or talks, tiny droplets of saliva or mucus are diffused into the air, which can be inhaled by another person.Once infectious particles reach the alveoli of lungs then a cell, called the macrophage, Swallow the TB bacteria.Then the bacteria are transmitted to the lymphatic system and bloodstream and spread to other organs.When the bacteria cause clinically detectable disease, you have TB.

Risk factors for TB include the following:1.HIV 2.low socioeconomic status,3.alcoholism,4.homelessness,5.crowded living conditions,6.diseases that weaken the immune system,7.migration from a country with a high number of cases,8.and health-care workers.